Greywater reuse towards sustainable water management

DESALINATION ELSEVIER

Desalination I56 (2003) 18 l-l 92 www.elsevier.comAocate/desal

Greywater reuse: towards sustainable water management Odeh R. Al-Jayyousi Civil Engineering Department, College of Engineering, Applied Science University, Amman I1 931 Jordan Fax: +962 (6) 523-2899; email: [email protected]/[email protected] Received 2 January 2003; accepted 15 January 2003

Abstract

The aim of this paper is to assess the role of greywaterreuse in sustainablewater management in arid regions. Moreover,it intendsto documentthe experienceof greywaterreuse in Jordan.Creywater(GW) is the water collected separatelyfrom sewageflow that originatesfrom clotheswashers,bathtubs,showersand sinks, but does not include wastewatertirn kitchen sinks, dishwashers,or toilets. Dish, shower, sink, and laundry water comprise 5040% of residentialwastewater.GW is used in groundwaterrecharge,landscaping,and plant growth.A case study on GW reuse in Jordan is presentedto shed some lightson its role in sustainablewatermanagement.To operationalizethis concept, wateris viewedas an economicgood and a finiteresourcethat shouldbe valuedand managedin a rationalmanner.The studyconcluded that currentenvironmentalpoliciesshouldaimto controlpollutionandto maximizerecyclingandreuse of GW withinhouseholdsand communities.DecentralizedGW/wastewatermanagementoffersmore opportunitiesfor maximizingrecyclingopportunities. Keyworak

Greywaterreuse; Sustainablewater management;Watermanagement;Jordan

1. Introduction Historically, domestic greywater reuse was practiced to conserve water. However, social and economic constraints prevented its further development and integration in the urban water systems [ 11. It is likely that new innovations in water management will eventually lead to substantial changes in lifestyle, particularly if the use of water as a transport medium for our domestic waste is reduced or eliminated [2].

The conventional paradigm of water/wastewater management was characterized as supplydriven, centralized and large-scale development. This approach led to over-exploitation or depletion of renewable water resources, mining of non-renewable groundwater resources and deterioration of water quality. The collection and disposal mind-set prevailed because of concerns over public health protection. Water-intensive and centralized sewer systems were built to

Presented at the European Conference on Desalination and the Environment: Fresh Waterfor All, Malta, 4-8 May 2003. European Desalination Society International Water Association. 001 l-9164/03/$-

See front matter 0 2003 Elsevier Science B.V. All rights reserved

PII: SO01 1-9164(03)00340-O

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remove wastewater from immediate environment of the communities using water as a transport medium. This paradigm is inadequate for sustainable water management. A need for a paradigm shift is necessary to ensure optimum utilization of resources [3-51. Wastewater and greywater (GW) recycling are emerging as integral parts of water demand management, promoting the preservation of highquality fresh water as well as reducing pollutants in the environment and reducing overall supply costs. Recent developments in technology and changes in attitudes towards water reuse suggest that there is potential for GW reuse in the developing world. GW represents the largest potential source of water savings in domestic residence. For example, the reuse of domestic GW for landscape irrigation makes a significant contribution towards the reduction of potable water use. In Arizona, for example, it is documented that an average household can generate about 30,000 to 40,000 gallons of GW per year [6]. This illustrates the immense potential amounts of water that may be reutilized, especially in arid regions like the Middle East. Domestic G reuse offers an attractive option in arid and semi-arid regions due to severe water scarcity, rainfall fluctuation, and the rise in water pollution. To ensure sustainable water management, it is crucial to move towards the goal of efficient and appropriate water use. GW reuse contributes to promoting the preservation of high-quality fresh water as well as reducing pollutants in the environment. Meeting different needs with the appropriate quality of water may prove to be economically beneficial and at the same time reduce the need for new supplies at a higher marginal cost. Mixing GW with rainwater is a viable practice; however, since rainwater is generally of high quality (COD<200 mg/l), the stochastic nature of rainfall events implies a large storage capacity is necessary for its optimum use [7]. Conversely, domestic GW often has a higher

pollutant load (up to 5000 mg/l COD) but is produced according to more regular patterns, which are simpler to exploit for the purposes of domestic reuse [8]. GW reuse can result in cost savings (to both the consumer and state water authority), reduced sewage flows and potable water savings of up to 3 8% when combined with sensible garden design [9]. The aim of this paper is to assess the role of RW reuse in sustainable water management in arid regions, particularly documenting Jordan’s experience in GW reuse.

2. Characterization of greywater GW is the wastewater collected separately from sewage flow from clothes washers, bathtubs, showers and sinks, but does not include wastewater from kitchen sinks, dishwashers, or toilets. Dish, shower, sink, and laundry water comprise 50--80% ofresidential wastewater. GW may be used in groundwater recharge, landscaping, and plant growth. Due to the fact that GW is usually generated by the use of soap or soap products for body washing, its quality varies according to source, geographical location, demographics and level of occupancy, as shown in Table 1. GW is relatively low in suspended solids and turbidity, indicating that a greater proportion of the contaminants are dissolved. Moreover, although the concentration of organics is somewhat similar to domestic wastewater, their chemical nature is quite different. The COD:BOD ratio may be as high as 4: 1 (very much greater than values reported for sewage). This is coupled with a deficiency of macro-nutrients such as nitrogen and phosphorus. The COD:NH,:P of GW has been measured at 1030:2.7:1, and this compares with 1OO:S:l for domestic wastewater. Hence, both the relatively low values of biodegradable organic matter and the nutrient imbalance limit the effectiveness of biological treatment [ 131.

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0.R Al-Jayyousi 1 Desalination 156 (2003) 181-192

Table 1 Typical composition of greywater from various sources Source Hand basin Combined Synthetic greywater Single personb Single family’ Block of flatsb Collegeb Large colleged “Total nitrogen.

COD (mg/l)

Turbidity (NTU)

109 121 181 110 -

263 371 -

-

33 80 96

40 146 168

_ Bob

(w4

256 -

69 25 14 76.5 20 59 57

bHolden and Ward [lo]. ‘Sayers [ll].

In sum, GW reuse helps to conserve and optimize the use of water resources. However, GW treatment and reuse are to be assessed in terms of technical feasibility, public health, social acceptability and sustainability.

NH3(mg/l) P (m.0

Total coliforms

9.6” 1 0.9

2.58 0.36 -

1.5x106 -

0.74 10 10 0.8

9.3 0.4 -

1x106 -

2.4

5.2x106

-

dSurendan and Wheatley [ 121.

r .-.

3. Conceptual framework for greywater reuse It is interesting to look at the dynamics of water/wastewater allocations and their uses. Governments allocate substantial amounts of money to develop, treat and transport water resources. On the other hand, more money is spent to collect wastewater, treat it and then transport it to distant places for potential uses. To address the externalities of this paradigm, attention is to be focused on small-scale and on-site treatment of waste/GW [ 141. The following conceptual framework for GW reuse is based on the closed-loop concept. This implies that GW is being managed and reused in a decentralized manner within the household, neighborhood, and/or community. The concept of closed loop in water demand management was documented by Bakir [ 15J. The main idea is to match water quality with appropriate water uses as shown in Fig. 1. In other words, GW may be allocated for appropriate uses

Fig. 1. Schematic diagram for a closed water loop for a residential building [ 151.

such as, irrigation, landscaping, toilet flushing, and groundwater recharge.

4. Treatment of greywater Based on the work of Nolde and Dott [ 161, GW from recycling systems should fulfill four criteria: hygienic safety, aesthetics, environmental tolerance, and technical and economical feasibility. In most countries, guidelines and standards for water reuse in buildings either do not exist or are being revised or expanded. In 1992 the US Environmental Protection Agency (EPA) published “Guidelines for Water Quality” that describes the treatment stages, water quality

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O.R. Al-Jayyousi / Desalination 156 (2003) 181-192

requirements and monitoring tools [ 171.According to the EPA, reclaimed water used for toilet flushing should undergo eventual filtration and disinfection. The effluent should have no detectable fecal coliforms in 100 ml of the treated water, a BOD of l mgl-’ whereby Cl, should be continuously monitored. Options for making safe use of GW as a source for irrigation are many and diverse. A key to successful GW treatment lies in its immediate processing and reuse before it has reached the anaerobic state. The simplest GW treatment consists of directly introducing freshly generated GW into an active, live topsoil environment. Many new technologies have been developed to treat GW. Some of these technologies include Planter soilbox design and pressure leach chambers. The major difficulty presented for treatment of GW is the large variation in its composition. Reported mean COD values vary from 40 to 371 mg/l between sites, with similar variations arising at an individual site. This has been attributed to changes arising in the quantity and type of detergent products employed during washing. GW quality is also subjected to dynamic variation. Significant chemical changes may take place over time periods of only a few hours. Table 2 shows a summary of water quality standards for domestic water recycling. The rationale for treating GW is based on biological characterization of GW. It has been documented that GW can contain at least 10’1 100 ml of potentially pathogenic microorganisms [ 18-201. It is also accepted that stored GW undergoes changes in quality which include growth in numbers ofmicro-organisms according to the limiting factors for each particular microorganism. Research has shown that counts of total coliform and faecal coliforms increased from 1O”-lo’/1 00 ml to above 1OS/100 ml within 48 h in stored GW from various sources. Of more concern is the potential infection route that GW

provides for viral infections. Viruses comprise a serious risk to health, which is amplified by the relatively low dose required to cause infection. In light of the amounts of GW that are possible for reuse and the viability of its application, many technologies have been developed. Processes range from simple systems in single houses to very advanced treatment schemes for large-scale reuse. Work conducted by the National Aeronautics and Space Administration demonstrated how bath and laundry water could be reused by passing the water through diatomaceous earth filters followed by activated carbon [21,22]. Model guidelines for domestic GW reuse in Australia have been prepared [22]. These cover hand basin toilets, primary GW systems (direct subsurface application) and secondary GW systems (mesh, membrane or sand filtration). The following is a description of the most common GW treatment technologies. 4.1. Basic two-stage systems Coarse filtration plus disinfection represents the most common technology used for domestic reuse in the UK. The generic process employs a short residence time so that the chemical nature of the GW remains unaltered and only minimal treatment is required. The coarse filter usually comprises a metal strainer. Disinfection is achieved using either chlorine or bromine, dispensed in slow release blocks or by dosing a liquid solution. Systems recently tested [ 111have shown a variety of water saving levels ranging from 3.4% to 33.4%. The basic two-stage system was designed to meet the less stringent reuse standards akin to those for bathing water, rather than the more conservative standards. The water thus remains high in organic load and turbidity, thereby limiting the effectiveness of the chemical disinfection process for two reasons. Firstly, GW contains flocculent particles above 40 mm in

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185

Table 2 Summary of water quality standards and criteria suitable for domestic water recycling (adapted from [ 121)

Bathing water Standards” USA, NSF USA, EPA Australia UK (BSIRA) Japan WHO Germany

Total coliform count/ 100 ml

Faecal coliforms

BOD, (mg/J)

Turbidity (NTU)

Cl, residual (mg/l)

pH

10,000(“~ 5000 -

2000’” loo@’ ~240 <4
-

-

-

6-9

45 10 20 -

90 2 2 -

1 -

-

10 -

5 -

-

6-9 -

500

20

l-2

-

6-9

Non-detectable
6-9 -

“Bathing water standards suggested as appropriate for domestic water recycling. (g), guideline, (m), mandatory. and these are known to reduce chemical disinfection capability because the disinfection cannot diffuse far enough into the floes to provide complete killing of pathogens. Secondly, organic matter in the water requires a disinfectant. In the case of chlorine, disinfectant byproducts such as chloramines and trihalomethanes are generated, which have a lower disinfectant capability and adversely affect human health. Additional problems occur due to the presence of detergents that are known to produce an odor in water at concentrations above 3 mg. Since physical processes achieve substantial clarification of water, they are reasonably effective in decreasing the organic pollutant load of GW prior to reuse, since this is to some extent associated with turbidity. The aesthetic quality of the product water is thus increased and problems associated with downstream disinfection encountered in the coarse filtration systems substantially ameliorated. On the other hand, simple filtration based on fibrous (cloth) of granular depth filter presents no absolute barrier to suspended matter, resulting in coliform breakthrough and a propen-

diameter,

sity for solids unloading whenever hydraulic shocks occur. Membrane systems offer a permanent barrier to suspended particles greater than the size of membrane material, which can range from 0.5 mm of microfiltration membranes down to molecular dimensions for reverse osmosis. The treated water is thus generally extremely low in turbidity below the limit of detection for coliforms, as shown in Table 3. On the other hand, the energy demand for membrane systems is substantially higher than that for depth filters: the data shown in Table 3 refer to tubular MFAJF systems, the most commonly used, which are operated at pressures up to 2.0 bar. Problems of poorly treated water quality have been reported with membrane systems treating GW water, as well as difficulties in effectively cleaning membranes. The residence time of the system has been identified as being a major cause for concern. Over extended time periods, the GW can become anaerobic, resulting in the generation of organic components which are less readily rejected by the membrane [lo].

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Table 3 Performance of sand filter and membrane filtration processes for greywater treatment ~.~_.~-___~~_._._~ ~__~__~__._~__~_~. ~ .~~~._. ~~~.~ ~_ ~

Influent” Post-sand filter Post-membrane Influent Post-membrane Pre-advanced oxidationb Post-advanced oxidationb Pre-coagulationd Post-coagulationd -

BOD, Ow4

COD (mg/l)

33.3 12.3 4.7 25-185 l-19 41 (TOC) 25 (TOC) ____

143 35.7 22.2 86-410 21-l 12 100 30

Turbidity __44.5 32.3 0.34 12-100 Cl 29.4 2.41

TC (cfu/lOO ml)

_._.._.__.~~~_____~.._~

0 E. Coli 2-310~10~ ND-2419 9x105 ND’ -

“Holden and Ward [lo]. bBasedon a 2 g/I concentration of Tio2 activated by an UV irradiation source. “Non-detectable. dBased on a ferric chloride dose of 30 mg/l.

The key factor constraining the economic viability of membrane systems is the fouling of the membrane surface by pollutants species. This increases the hydraulic resistance of the membrane, thereby commensurately increasing the energy demanded for membrane permeation and/or decreasing the permeate flux. 4.2. Biological systems

Biological treatment is required to remove biodegradable material, especially for systems that include large distribution networks such as hotels or community-based recycling schemes. The benefits of biological and physical treatments are combined in processes such as membrane bioreactors (MBR) and biologically aerated filters (BAF), which are small footprint processes capable of producing high-quality effluents.

BAFs combine depth filtration with a fixed film biological reactor. As such, they present no absolute barrier to suspended materials and thus do not substantially disinfect the water. MBRs combine an activated sludge reactor with a

microfiltration membrane, and have been successfully employed in Japan for GW recycling in office blocks and residential buildings [23]. The MBR process can be configured with the membrane placed within the reactor (submerged MBR) or by externally to it (sidestream MBR). The two systems show similar biological performance but membrane permeation differs between them. The external systems are run at higher transmembrane pressures, producing higher flow rates that exacerbate fouling problems and thus necessitate regular cleaning. The internal systems are operated hydraulically, generating much lower flow rates which are, however, stable, thereby reducing membrane cleaning requirements to once in every 6 months as opposed to monthly, weekly or even daily for the side steam configuration operating in cross-flow mode. The complexity of the technology applied is generally commensurate with the scale of the recycling scheme. Cost implications have meant that single-house systems are largely restricted to coarse filtration devices with downstream disinfection. The current emphasis is on simple and

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reliable systems. Installations in colleges and small offices have focused on physical or simple biological systems, and these have been shown to be far more economically viable than singlehouse systems. The scheme in Lt.&borough, for example, has reported a payback time between 5 and 10 years [12]. More than 20 units have been tested in Jordan, Tafileh Governorate. Two types of GW systems were installed and are being monitored [24], and a preliminary environmental assessment of GW in Jordan was conducted [4]. 5. International

experience of greywater reuse

On the global scene, Japan, the US and Australia maintain the highest profile in GW reuse [8]. Other countries involved in active GW research and applications include Canada, the UK, Germany and Sweden [14,25-271. On the regulatory and legal arena, GW reuse has gained a degree of acceptance in the US and Australia. This is evident in the California Pumping Code and in the Australian general guidelines for domestic GW reuse [8]. At the regional level, Saudi Arabia, Cyprus, and Jordan have introduced GW systems to optimize water use. However, guidelines and technical specifications are still underway. It should be noted that each country has a different reason for the adoption of GW reuse. For example, the Japanese reuse initiative is driven by the demands of a high population density and small land space, while the US, Australian, Saudi Arabian and Jordanian initiatives are a direct response to drought conditions and the unregulated uptake of domestic GW reuse for garden irrigation. However, it seems that certain GW reuse initiatives are not focused directly upon attaining a more sustainable future; rather they are short-term reactions to water scarcity. The main use for GW in Germany is for toilet flushing, irrigation and garden plants. In terms of

187

treatment of GW, some manufacturers of GW systems assume a mechanical treatment of the GW to be satisfactory [28], whereas others claim a more advanced treatment technology to be necessary. GW recycling plants have proved their efficiency and applicability in practice for almost 10 years. Current on-site treatment systems have generally adopted the technology of conventional activated sludge plants for large treatment systems. This is understandable because the effluent standard for garden surface irrigation is a chlorinated effluent containing not more than 20 BOD130SS. Differences that can be observed are the insertion of a trickling filter in the aeration chamber to cope with variable flows and the infrequent removal of sludge. The anaerobic decomposition of sludge takes place in the first settling chamber. Hyper-chlorination of ammonium in secondary effluent theoretically removes N by oxidation to nitrogen gas. Following successful operation of these systems and achievement of the set criteria, guidelines for service water reuse were then first introduced in Germany in 1995 on a local level by the Berlin Senate Department for Building and Housing. Parameters were defined among others for BOD, <5 mg/l’, total coliforms ~100 ml-‘, faecal coliforms ~10 ml-’ and Pseudomonas ueruginosa
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O.R. AI-Jayyousi /Desalination

toilet flushing requirements shows a natural affinity at about 30% of the total water use [13,29-3 11.The viability of internal recycling is to some extent contingent upon there being substantial differences in water quality and quantities demanded for different operations [1 I]. On the other hand, in Western Australia, five particular methods were being tested by the Institute for Environmental Science at Murdoch University to achieve fully integrated permaculture development [32]. Model guidelines for domestic GW reuse in Australia have also been prepared [22,33]. These covered hand basin toilets, primary GW systems (direct subsurface application) and secondary GW systems (mesh, membrane or sand filtration). For primary systems the guidelines adopted the Californian approach of requiring the use of a surge tank with a screen to remove lint and hair. 6. Greywater ewe: Jordan’s experience Jordan’s water resources are characterized by vulnerability and variability. Due to its uneven topographic features, the distribution of rainfall in Jordan varies considerably with location. Rainfall quantities vary from 600 mm in the northwest to less than 200 mm in the eastern and southern deserts, which form about 91% of the surface area. The average total quantity of rainfall is approximately 7200 MCM/y, and it varies between 6000 and 11,500 MC&I/y. Approximately 85% ofthe rainfall evaporates, and the rest flows into rivers and wadis as floods flow and recharge groundwater. Groundwater recharge amounts to approximately 4% of the total rainfall volume, and surface water amounts to approximately 11% of total rainfall volume [3,41. Jordan is facing a chronic imbalance in the population-water resources equation. The total renewable freshwater resources of the country amount to an average of 750 MCM/y. The population in 1997 was estimated at 4.6 million,

156 (2003) 181-192

and growing at an annual rate of 3.5%. The per capita of water was 160 m’/y in 1997. The renewable water resources falls short of meeting actual demand, which translates into an increase of food imports where the deficit in food balance reached $110 per capita in 1996. Despite the huge investment in the water sector, a considerable water deficit still faces Jordan. The water deficit for all uses is projected at 408 MCM/y in the year 2020 [34]. The long-term safe yield of renewable groundwater resources has been estimated at 275 MCM per year. Some of the renewable groundwater resources are presently exploited to their maximum capacity and in some cases beyond safe yield. The average resident of the capital city of the Kingdom of Jordan currently receives less than 100 led, all delivered only 1 or 2 days a week. Since 1993, Jordan has put forth substantial efforts towards the remedy of the water situation in the country. As a result, water policy reform was initiated. It aimed to restructure institutional frameworks, strengthen capacities, rationalize strategies, improve financial viability and widen public awareness and participation. Moreemphasis was put on increasing the commercial focus of operations. The concept of separating national infrastructure from service delivery has also become an acceptable option, and the need to mobilize all available resources, including an increased role of the private sector in systems operation, was recognized [3,4]. A pilot project for GW reuse was implemented in Ain Al-Baida, Tafileh Governorate [24,35]. The main use for GW in the project area is for garden farming in rural areas. The technology used ranges from direct use of GW at its original state to adopting a preliminary (separation of fat and grease) and secondary automated treatment system, as shown in Fig 2. Faruqui and Al-Jayyousi [35] documented the findings of GW reuse in Tafileh, Jordan. The study revealed the following:

0. R. Al-Jayyousi / Desalination 156 (2003) 181-l 92

189

Portable water backup w ith air gap I

Automatic

1

To subsurface dr io irr iaation fieid ’

back-

Electronic controller

Gravity

tank

Can be located under house, outside, or underground

1. The organic content of the GW samples, measured by biological oxygen demand (BOD,), ranged from 275 mg/l to 2287 mg/l. This is a little higher than typical BOD, values for GW, but not surprising given the low water consumption in Ain El Baida. 2. The detergent concentration, measured by the methylene blue alkyl sulfonate (MBAS), ranges from 45 mg/l to 170 mg/l, consistent with the use of sulfonate based dishwashing detergent. 3. The pH of the baseline tap water was 8.3 5. Three of the GW samples had a pH higher than 8.35, likely due to the presence of dishwashing detergent or hand soap containing caustic soda, which is a strong base. The other three samples had a pH lower than 6.7, which may have resulted from the presence of foods high in acid such as tomatoes and cooking oil. This is a positive effect because the higher the pH, the higher the alkalinity. 4. The average EC of the GW samples was 818 deciSemens/m (ds/m), and varied from 457 ds/m to 1135 ds/m. The salinity of the tap water is 594 ds/m. The salinity of the samples was a little higher than the medium salinity in the

Fig. 2. Automated greywater system.

baseline tap water because of the addition of salts contained in food particles. Where the GW salinity was lower than that of the tap water, the households diluted the GW with rainwater. 5. The average sample SAR was about 3 and ranged from 1.0 to 6.8. The tap water SAR was only 0.83. Higher detergent content corresponds with higher SAR values, indicating the detergent and soap contains sodium that is increasing the alkalinity of the water. 6. The average EC of soil irrigated with GW was 2.76 ds/m, varying from 1.01 ds/m to 6.78 ds/m. The average salinity of the baseline soil was 2.57 ds/m, with a range from 0.93 ds/m to 4.2 1 ds/m. 7. The average SAR of the samples was 3.7 and varied between 1.71 and 5.59. The average SAR of the baseline soil was 2.84 and ranged from 1.54 to 4.14. The SAR of alkaline soils generally exceeded 6, meaning the soil irrigated with GW is good for the cultivation of most crops. To follow up, a GW reuse and treatment project in Tafileh, Jordan, was implemented by the Islamic Network for Water Development and

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O.R. Al-Jayyousi / Desalination 156 (2003) 181-192

Table 4 Greywater quality parameters before and after treatment Sample type

PH

TSS

O&G

BOD

ABS

(FC/lOOml)*10

Raw greywate? TGW samplelb TGW sample 2 TGW sample 3 TGW sample4 TGW sample 5” Average TGW Percent reductiond

6 7 6 6

316 42 158 517

141 20 13 50

1500 106 680 1011

3

56

5

99

8 6 0

171 189 0.40

8 19 0.86

66 392 0.74

101 20 89 99 21 3 46 0.54

7 5 6 6 2 4 5 0.34

“These values represent weighted means of raw greywater from households. bTGW: Samples 1 through 4 represent treated greywater (TGW) for households. “Sample 5 represents treated greywater from an institutional building. dThese values represent the rate of change between two means (raw and TGW).

Management and was funded by the International Development Research Center. GW quality parameters are shown in Table 4. The above parameters for 25 users in the project area, Tafileh, Jordan, show the degree of effectiveness of the treatment of GW. It is evident from Table 4 that the reduction rates (for raw GW vs. treated greywater) for TSS, oil and grease, and BOD were 0.4, 0.86, and 0.74, respectively. However, the variations in GW characteristics are substantial due to different social habits with respect to dish washing and use of detergents. 7. Conclusions

and recommendations

Greywater reuse presents a potential option for water demand management and also contributes to reducing fresh water use for irrigation. To ensure water sustainability, GW reuse needs to be coincidental with water-sensitive garden design and growing food at home and public open spaces. When GW is to be used for irrigation, there may be an imbalance between plant requirements for the nutrients and the seasons,

with a higher requirement in the warmer months than the colder ones. Rather than removing the nutrients, an alternative is to store the nutrients in the soil. GW reuse needs to be seen in terms of its contribution to sustainable water development and resource conservation without compromising public health or environmental quality. The following conclusions can be drawn: GW guality varies considerably and thus appropriate technology is to be selected to suit the users’ needs and utilize local knowledge. Residence time in systems dramatically affects the characteristics of GW. Simple two-stage filtration and chemical disinfection systems remove coliforms but remain high in turbidity and organic pollution. Advanced filtration systems reduce all components of GW but do not reliably meet all the water recycling standards. References [l]

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